Hardening spring by internal oxidation



Jan. 14, 1964 c. D. COXE HARDENING SPRING BY INTERNAL OXIDATION Filed Oct. 8, 1959 INVENTOR. Charles J). (3 9( M W mg;

M AIZOf/VEYS United States Patent 3,117,894 HARDENIWG SPRING BY INTERNAL @XHDATIQN Charles D. Quxe, Fairfield, Conn, assignor to Handy and Harman, Fair'field, Qonn, a corporation of New York Filed Get. 8, 1959, Ser. No. 845,227 3 (Zlaims. (@l. 148-1l.5)

This invention relates to springs and particularly those requiring high electrical or thermal conductivities.

In spring members which are normally under load, such as electrical relay springs, vacuum tube clips, spring collet fingers and the like, it is desirable to have a spring material with high electrical or thermal conductivity, as the service may require. Such a spring must be able to withstand high temperatures and yet retain its resilience and high elastic limit.

It is known that metals such as silver or copper can be alloyed with small amounts of metals having a high heat of oxide formation, such as magnesium, beryllium, or aluminum, and then can be hardened by heating the alloy in an oxidizing environment to form internally oxidized alloys having high strength, conductivity, and extraordinary ability to retain a substantial measure of these physical properties at elevated temperature. Their room temperature properties are unaffected by heating to temperatures that would completely anneal or soften conventional metallic alloys not internally oxidizable. Such internally oxidized alloys are comprised of substantially pure metallic matrices having dispersed therein very fine (submicron size) oxide particles.

While the tensile properties of such internally oxidized alloys are such as would make their use in spring members desirable, it has been found that such springs are subject to spontaneous cracking under constant load, with practically no elongation.

One of the objects of the invention is to provide a process for making spring members which will not spontaneously crack or fail when under constant load and will not lose their resilience after heating to temperatures that would completely anneal conventional spring materials.

Another of the objects of the invention is to provide a spring member which can be used under a continuous load without failure.

In one aspect of the invention, a polycrystalline metal alloy capable of being internally oxidized is subjected to an oxidizing environment. The internally oxidized polycrystalline alloy is plastically deformed 50% or more, and then formed into a spring. After plastic deformation, the alloy preferably is subjected to an annealing operation. If the plastic deformation is at least 75%, it is not always necessary to anneal.

These and other objects, advantages and features of the invention will become apparent from the following description and drawings.

In the drawings:

FIG. 1 shows an enlarged view of a strip of metal and schematically shows plastic deformation thereof;

FIG. 2 shows a test strip of metal bowed into a spring;

FIG. 3 is similar to FIG. 2 except the spring is shown broken;

FIG. 4 shows one use of a spring member made in accordance with the invention, such merely being an example.

The invention involves springs made of solid solution alloys which consist of relatively non-oxidizable solvent metal alloy capable of diffusing oxygen and solute metal which forms stable oxides. Internal oxidation is accomplished by subjecting such a solid solution alloy or internally oxidizable alloy or material to an environment of an oxygen containing gas or media at elevated temperatures. Such an environment is one that is oxidizing to the solute metals but non-oxidizing to the solvent metals. The hardening of the alloy is the result of internal oxidation wherein very small refractory oxide particles are precipitated in the matrix. I

As an example, a leaf spring of the alloy Ag 99.5% Mg 0.3% Ni 0.2% may be prepared and rolled to a strip 0.012" thick as shown in edge view in FIGURE 1. This spring strip may then be hardened by heating in air at 1350 F. for about 45 minutes. If this spring is then sprung into a bow and restrained at the ends so that the outer fibers of the spring are under tension, the spring will frequently fracture, as in FIGURE 3, on standing at room temperature, and will fracture in almost every case when subjected to temperatures in the range of 500 to 1000 F. while under load. Attempts to alleviate cracking of the spring by reducing the oxide content undesirably lowers the tensile properties and this is not satisfactory for a spring normally under load.

As one example of the invention, a leaf spring was made of an alloy composed of Ag 99.5% Mg 0.3% Ni 0.2% rolled to a strip 0.048" in thickness and then hardened by heating in air at 1350 F. for about 9 hours, the thicker material requiring a longer time for oxygen penetration. It was then cold rolled to 0.012" and tested by being sprung ito a bow, as seen in FIG. 2. It was found to no longer be crack sensitive and to withstand heating to 1000 F. under load without failure. An illustration of a failed spring is seen in FIG. 3. The invention has been found to be particularly efiicacious when the oxidizable metal content is over 0.2%. Annealing can be carried out at a temperature in the range of 1000 F. to 1400 F.

The effect of cold working various amounts subsequent to oxidation is shown in the following table which tabulates the tensile properties and cracking performance of spring strips that have been cold Worked various amounts after hardening. In these tests, the bowed leaf springs were held 20 hours at room temperature. Those surviving this test were then placed in an oven at 500 F. for 6 hours, where additional failures occurred. The survivors were then heated to 1000 F. for 6 hours, where additional failures occurred. Those failing at room tempera ture were termed poor, those failing at 500 F. fair, those failing at 1000 F. good, and those surviving the 1000 F.

test excellent. The test results under this procedure, together with strengths obtained, were as follows:

tial pressure that will selectively oxidize Be without caus ing the copper to scale excessively.

Table 1 Testing Dirce- Yield Tensile Treatment Treatment tien Strength Strength Elong, Cracking No. Longil,000 XLOOO percent Test tudinal p.s i p.s.i. or Trans- VGI'SG I Cold Rolled .000 to .012"; Oxidized L 75.0 79.0 7 Poor.

1,350 F. T 64.6 06.5 a Good. II Cold Rolled .600" to .010; Oxidized {L 78.5 84.1 2 Poor.

1,350 n; cold Rolled .012 (25%). T 69.1 72.8 3 Do. nr IIplusanncal1,350F 5 1V Cold Rolled .600" to .024; Oxidized {L 77.1 82.8 2 Excellent 1,350F.; 051a Rolled .012" 50%). Qt 53.0 1 51 t r r, v IV plus annea11,350 i g f VI Cold Rolled .600 to .048; Oxidized {L 67.1. 70.7 2.5 Do. 1,350 F.; Cold Rolled .012 (75%). T 07. 0 72.1 3 Do. vn vr plus anneal 1,375 F $5 ff 53:

These tests were repeated on material which, (11111115 The tendency for delayed brittle fracture in stress, as the initial cold rolling before oxidation, was annealed in oxidized (not cold worked) alloy springs increases as the process before the last 50% reduction prior to oxidation oxidizable element increases, or as the strength increases. to reduce the directionality of the strength properties, i.e., Generally, when the as oxidized strength is well below to produce less preferred orientation of crystallographic 60,000 p.s.i., delayed brittle fracture does not occur, and axis in the direction of rolling. when it is Well above 60,000 p.s.i., it will nearly always Table 11 Testing Diree- Yield Tensile Treatment tion, Strength Strength Eleng., Cracking N Treatment Longi- 1,000 X1, 000 percent Test tudinal p.s.i. p.-s.i. or Trans- Verse r 70.0 0 I- n 1 5 fi}, 11 $3 1? L 75. 0.5 2 II-A 25% OR. after oxidizing s. {T 3 S08 3 1,0030

A J III-A 11-. plus 1,350 anneal g g rv-A 50% m oxidizing 5 ff' f TY-1 553? 73.4 74. V-A IV-A plus anneal 1,350 F 78. 5 gg gf f' vr-x 75% on. and oxidizing l1? 3- A L 72.5 74.5 Do. VIIA VI-A p1us1,350 anneal 8M 7 m It will be noted that cold rolling after oxidrzn. occur. Hence the invention is particularly useful for reduced resistance to cracking, eduction nnproved 59 springs stronger than 60,000 psi, and especially in springs it in some cases, and 50% reduction plus annealing elimlhaving 70,000 p.s.i. tensile strength. The lower limit of nated it as did 75% reduction and 75% reduction plus magnesium in silver for which the invention is eilective nn li g, under any condition is about 0.1%. Similarly, it appears Heretofore, the cracking of internally oxidized polythat about 0.05% Be in copper is a minimum alloy that crystalline metal has seriously hindered its use as springs. will benefit from the invention. When Be in copper ex- This improvement makes possible much more extensive ceeds about 0.25% and Mg in silver exceeds about 0.35%, use of springs of such material at elevated temperatures the oxidized alloy becomes too brittle to cold work satisand at higher loads. factorily. Thus, in an Ag alloy, the Mg should be be- The process of severe plastic deformation thus overtween about 01% and 5% In a Cu allay of the comes a basic defect in internally oxidized polycrystalline 60 type described, the Be Should be betv/een about 0.05%

alloys, but it is important that the plastic deformation be substantiala little, 25%, under the above experimental conditions was worse than none. The limits may differ for other alloys and processing details.

Annealing appears to be necessary to avoid brittleness in 50% cold worked material, but not in 75% cold worked material. However, if a spring member is to be further shaped or formed after cold rolling, the added ductility obtained by annealing will facilitate operations such as bending to the desired form of leaf springs, or the winding of coil springs. Flat, cantilever type springs, cold worked 75%, need not be annealed.

Similar results were obtained with an alloy of coppewith 0.1% to 0.2% of beryllium, oxidized at l6=00 F. in a pack of C11 0 which serves to furnish oxygen at a parand 0.25%.

Other matrix metals capable of having their solute metal internally oxidized may be used, such as for example palr ladium and nickel.

What is claimed is:

1. The process of making a spring of polycrystalline metal alloy hardenable by internal oxidation, said alloy having a solvent metal selected from the group consisting of silver, copper, palladium and nickel and an oxidizable metal dissolved therein in an amount ranging between 0.05% and 035%, comprising the steps of subjecting said alloy at elevated temperature in the range below the melting point of said solvent metal and above the minimum temperature for effective oxidation of said oxidizable metal to an oxygen containing environment to oxidation harden said alloy, decreasing the cross-sectional area of the oxidation hardened metal by cold working at least 50%, annealing the cold worked oxidation hardened metal, and forming a spring therefrom.

2. The process of making a spring of polycrystalline metal alloy hardenable by internal oxidation, said alloy having a solvent metal selected from the group consisting of silver, copper, palladium and nickel and an oxidizable metal dissolved therein in an amount ranging between 0.05% and 0.35%, comprising the steps of subjecting said alloy at elevated temperature in the range below the melting point of said solvent metal and above the minimum temperature for effective oxidation of said oxidizable metal to an oxygen containing environment to oxidation harden said alloy, decreasing the cross-sectional area of the oxidation hardened alloy by cold working at least 75%, and forming a spring therefrom.

3. The process of making a spring of polycrystalline metal alloy hardenable by internal oxidation, said alloy having a solvent metal selected from the group consisting of silver, copper, palladium and nickel and an oxidizable metal dissolved therein in an amount ranging between 0.05% and 0.35%, comprising the steps of subjecting said alloy at elevated temperature in the range below the melting point of said solvent metal and above the minimum temperature for efiective oxidation of said oxidizable metal to an oxygen containing environment to oxidation harden said alloy, decreasing the cross-sectional area of the oxidation hardened alloy by cold working at least annealing said alloy, and forming a spring therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 2,015,509 Austin Sept. 24, 1935 2,493,951 Mari et al Jan. 10, 1950 2,539,298 Doty et a1 Jan. 23, 1951 2,932,595 Pfluum Apr. 12, 1960 FOREIGN PATENTS 542,630 Canada June 23, 1951 533,137 Canada Nov. 13, 1956 OTHER REFERENCES Transaction AIME, vol. 147, pp. 205-221, 1942. 

1. THE PROCESS OF MAKING A SPRING OF POLYCRYSTALLINE METAL ALLOY HARDENABLE BY INTERNAL OXIDATION, SAID ALLOY HAVING A SOLVENT METAL SELECTED FROM THE GROUP CONSISTING OF SILVER, COPPER, PALLADIUM AND NICKEL AND AN OXIDIZABLE METAL DISSOLVED THEREIN IN AN AMOUNT RANGING BETWEEN 0.05% AND 0.35%, COMPRISING THE STEPS OF SUBJECTING SAID ALLOY AT ELEVEATED TEMPERATURE IN THE RANGE BELOW THE MELTING POINT OF SAID SOLVENT METAL AND ABOVE THE MINIMUM TEMPERATURE FOR EFFECTIVE OXIDATION OF SAID OXIDIZABLE METAL TO AN OXYGEN CONTAINING ENVIRONMENT TO OXIDATION HARDEN SAID ALLOY, DECREASING THE CROSS SECTIONAL AREA OF THE OXIDATION HARDENED METAL BY COLD WORKING AT LEAST 